Introduction of small interfering RNAs (siRNAs) into cells with transfection reagents results in potent and specific gene silencing by RNA interference (RNAi). Unfortunately, while siRNA-based drugs represent a potentially significant therapeutic paradigm, the ability to apply this technology to human disease has been impeded by the absence of efficient and non-toxic in vivo delivery systems. We recently developed a novel configuration of covalently modified RNAi compounds that do not require a delivery vehicle to enter cells and have improved pharmacology compared to traditional siRNAs. We term these compounds "self-delivering rxRNA" or sd-rxRNA." The objective of this proposal is to synthesize a novel panel of second generation sd- rxRNA compounds with improved potency and pharmacology by incorporating modified nucleotide bases with lipophilic moieties. A panel of lipophilically modified nucleotide phosphoramidites (pre-cursor monomers) using position 5 of a uracil will be synthesized for initial screening. These lipophilic monomers will be incorporated into an array of RNAi compounds that will be tested for enhanced potency in biological systems. Completion of this project is expected to develop a next generation of self-delivering rxRNA compounds with at least an order of magnitude better potency and improved pharmacology that can be used to develop RNAi drug candidates in multiple therapeutic areas.